Engraving machines such as bench top pantographs and computer controlled engraving machines utilize engraving tools called engraving cutters and burnishers. These tools comprise an engraving quill having a long circular cylindrical shaft with a cutter or burnisher mounted at one end thereof.
These quills are provided with a holder or holding collar sometimes called a cutter knob which is threaded at the bottom end for securing it to the cutter spindle mechanism of the engraving machine. Prior art quill holders are provided with a set screw and are roughened or knurled over the outer surface so that they may be rotated around and moved up and down the shaft of the engraving quill to meet the requirements of various machines and various thicknesses of materials to be engraved. Thus, the shaft of the quill is moved in the holder until a correct position is reached and the set screw is then tightened. Unfortunately, during high torque engraving, especially with high speed machines, the set screw engagement of the shaft may not be sufficient to keep the shaft from rotating within the holder. Repeated tightening of the set screw to secure a better grip causes distortion of the quill holder so that it becomes eccentric about the quill shaft. This sets up a vibration in the spindle of the engraving machine.
When used during high spindle rotation, the single set screw often is not sufficient to hold the harden cutter shaft. Repeated tightening of the set screw produces excessive pressure that causes distortion of the cutter head bore which again sets up undesirable vibration.
In addition, repeated tightening of the set screw permanently distorts the shank, unless very high strength carbide is utilized. Low carbon steel shafts become permanently marred and it becomes difficult to set the set screw and the knob at the proper position. The shafts often rust permanently fixing the set screw and the holder or knob to the shaft.
Diamond tip quills or cutters are widely used with a soft steel shank. While these do not generally require rotation of the tool, they do require down feed pressure of the tool and again often the set screw point pressure is not sufficient to securely hold the tool in place. On the other hand, solid carbide quills require repeated retightening of the set screw because of the high spindle rotation and weight of the tool.